1. Field of the Invention
This invention is related to the field of electro-optical systems in general and to the use of liquid crystals in electro-optical systems in particular.
2. Description of Prior Art
The utilization of nematic liquid crystals in the fabrication of electro-optical devices has been well established. For certain applications, it is desirable to orientate the directors of these crystals such that they are perpendicular to the surface of the substrates upon which they are placed.
Prior art processes for aligning liquid crystals included the use of either soluble ionic alignment agents or polymeric surface coatings.
Ionic aligning agents included tetraalkylammonium salts (U.S. Pat. No. 3,656,834 by I. Haller et al dated Apr. 18, 1972), barium stearate (I. Haller, Appl. Phys. Lett. 24, 349[1974]), or lecithin (F. J. Kahn et al, Proc. IEEE 61, 823[1973]).
The use of polymeric silicone coatings to align liquid crystals has been reported by Kahn, et al., loc. cit. as has the use of a plasma-polymerized film (J. C. Dubois et al. Appl. Phys. Lett. 24, 297[1974]).
A soluble polyamide has also been used to align liquid crystals (W. Haas, et al., Phys. Rev. Lett. 25, 1326[1970]).
Each of the alignment processes disclosed above have been shown to yield orientated liquid crystals with some significant limitations. In the case of ionic alignment agents, the undesirable characteristic is the conductivity of the resulting mixture. Devices fabricated from liquid crystals orientated via a polymeric aligning agent have exhibited slow response times and in some cases poor alignment stability.
This invention allows one to fabricate electro-optic devices exhibiting the desirable characteristics of prior art and devices having orientated liquid crystals without the undesirable characteristics mentioned above.